Hearing aid devices, or hearing aids, cannot correct hearing loss but are an aid that makes external sounds more assessable through amplifying them. However, hearing aids use microphones, electronic resistors, amplifiers and other electronic components. These components all produce noise and heat that is perceptible by the user. The volume of these background noises can be as loud as that of ordinary conversation taking place a meter away from a hearing aid user. Such noises are extremely annoying and uncomfortable to the hearing aid user, even when the surroundings are actually very quiet. Contrary to the common assumption that hearing impaired people cannot hear these white noises, survey and experiments show that most people, including hearing aid users, are quite sensitive to background white noises. Moreover, while hearing impaired people generally have difficulty hearing conversations and other sounds around them, they can certainly hear high decibel noises of various frequencies.
Current hearing aids on the market have a number of common problems and defects. There are currently three types of commonly used hearing aids now: body worn hearing aids, behind-the-ear (BTE) hearing aids, and in-the-ear (ITE) hearing aids.
With body worn hearing aids, the device amplifies background noises while making the sound signals loud enough for the user to hear. Such noises are continuous and of very high decibels (dB), usually 55 dB or more, which is at a similar volume to that of a person speaking at normal volume from one meter away from the aid user. Such background noises are a nuisance to the aid user, especially when the surroundings are very quiet. The hearing aid's sound sensor (e.g., a microphone) is usually placed in the device's case and any contact with the case, such as friction with clothing, accidental touch by hand, etc., tends to produce irritating high volume noises as a result of amplification by the hearing aid device. Volume adjustment often is achieved through a mechanical potentiometer via a turning knob; therefore volume control is difficult to be precise. Improper use of the body worn aid devices therefore tends to result in high dB feedback noise. Further, earphone used in a hearing aid device is usually the moving-iron type that produces annoying and uncomfortable high frequency sounds and also causes sound distortion. Sound generated by such feedback often is a squealing/whistling high frequency sound that can cause further hearing impairment. Occlusion effect is a common complaint for users of conventional body worn hearing aids.
With BTE hearing aids, the aid amplifies background noises while it makes the sound signals loud enough for the user to hear. Such amplified noises are continuous and of very high decibels (dB) (usually 55 dB or more, at a similar volume to that of a person speaking from one meter away from the aid user). They are a real nuisance to the aid user, especially when the surroundings are very quiet. Volume adjustment is achieved through a micro mechanical potentiometer via a turning knob. Because the mechanism often is very tiny for a behind-the-ear (BTE) hearing aid device, it is very hard for the user to set the volume at the desired level. Because of the structural design of the BTE aid, the microphone and the loudspeaker are placed close to one another so the earphone must be plugged tightly in the user's outer ear; if not, the sound amplifying mechanism tends to produce high dB feedback noises that can cause further hearing impairment. The earphone uses the moving-iron type loudspeaker that produces ear-splitting high frequency sounds, another nuisance to the user. Because the battery used generally is required to be tiny so it can fit into the small size of a BTE aid device, battery lift is short. As a result, the user has to change the battery frequently, which is a cost concern. Occlusion effect is also a common complaint for users of conventional BTE hearing aids.
ITE hearing aids are custom made to fit each individual's ear and they are very expensive. Because the components are tiny, normal maintenance is more complicated, therefore not really convenient for elderly users. When such an ITE device malfunctions, e.g., due to defects or damages, repair time tends to be long and cost is also high. Battery life is short and battery change is frequent, which is a cost concern. The volume adjustment mechanism is micro and tiny; as a result it is not convenient for the user. As a design requirement, ITE hearing aids generally must fit perfectly in the user's outer ear bawl to prevent sound leaking. However this tight fit condition often causes discomfort. Venting also produces high dB feedback noises that can cause further hearing impairment. ITE earphones use micro moving-iron-type loudspeakers that may cause sound distortion. Occlusion effect is a common complaint for users of conventional ITE hearing aids.
Current noise elimination technology digitally processes analog signals (i.e., sound signals). To do so, samples must be selected from the input sound signals. However, no matter how fast or how precisely samples are taken, the stored data is never the same as the actual sound signals. Digitalization cannot duplicate precisely and completely the original signals. This distortion caused by digitalization is called “quantizing distortion”. Processing digital signals relies on the digital circuit's working frequency (or sampling frequency). In order to keep the sampled signals substantially the same as the input sound signals, sampling frequency must be set high. However, high frequency necessitates increased electrical current, which in turn leads to high power consumption. Digital technology can eliminate some noise, but digital noise elimination generally is based on certain algorithms that are implemented as computer programs developed by a programmer. Since there are numerous kinds of noises in the real world environment, it is generally not possible to include all possible scenarios in one or a small number of algorithms. Current technology of digital filtering and frequency compensation tend to make the original and natural sound signals differ greatly from those a listener has been exposed to and used to. Consequently the processed sound signals may cause perception problems or mental/physical discomfort.
Current analog technology used for noise elimination uses various electronic techniques, especially analog filters. However, because sound signals are of diverse noise frequencies, it is extremely difficult to determine a priori while designing the filter which range of frequencies should be eliminated. Moreover, in the process of filtering, certain frequencies in normal and natural sounds will be faded out or eliminated altogether, which leads to sound distortion. Sound distortion usually causes difficulty in detecting and distinguishing sounds, especially for people who suffer from hearing problems.
It is known to use electronic techniques to deal with feedback noise. The following are some examples, which all have their own disadvantages and difficulties.
Frequency Shift: A 2-8 Hz frequency shift may be performed on the microphone signals so that when the microphone receives sound signals from the speakers, those signals generate reduced feedback. However, frequency shift cannot eliminate feedback noise entirely and typically increases audibility of the original sound by only about 6 dB.
Phase Modulation: In a self-induced feedback in an audio system, the feedback loop (return circuit) is a regenerative one. If sound signals from the microphone are processed by phase modulation, conditions for feedback self-excitation will be broken. However, high level phase modulation will distort sound effect and sound signals will sound unnatural to the listener.
Time Delay: Signals from the microphone may be recorded and played back after a time delay. Time delay can prevent feedback self-excitation in the audio system, no matter how loud the sound volume is tuned. However, time delay can only be used to prevent feedback when the signal from the microphone is very brief or in situations where the time delay does not cause perception issues. It is not suitable for use during conversation, due to the time delay between lip movement and sound perception.
Feedback Sensor: Feedback sensors can be used to decrease the amplifying effect of an amplifier. However, using a feedback sensor usually makes the sound volume too low.
The forgoing creates challenges and constraints for providing sound processing devices addressing the aforementioned difficulties and deficiencies. There remains a need for improving performance of sound processing devices, for example hearing aids, especially in terms of reducing feedback to improve hearing aid performance and reduce the likelihood of further hearing damage. It is also important that these sound processing devices be low cost, easy to maintain and have acceptable real world performance. It is an object of the present invention to mitigate or obviate at least one of the above mentioned disadvantages.